I currently have a Alpine cda-117 HU and a Alpine KTP-445 power pack amp 45rms x 4. Looking for a set of 6x8 speakers for the rear. Debating between two models, the
Infinity Reference 6832cf (60rms power) and Infinity Kappa 682.9cf (100rms power). Price is not a factor in my decision. I was thinking since the reference speaker is closer to the rms power of the amp, it will sound better and louder? Anyone have any input on this? Oh and I plan on using the other two channels on the amp later for front speakers.

 

Ideally the amps RMS wattage should be a little more then the speakers continuous power handling, [RMS], " it's better to be overpowered then underpowered"

Also keep in mind the Infinity speakers you list are 2 ohm, I am not sure if the Alpine KTP-445 is stable below 4 ohms.

Question... why are you using 6x8 speakers?

You should also be spending your time and money on front speakers, for good SQ in a car, rear speakers are not even needed, and if yo do want rear speakers they should be mid-range/mid-bass drivers, NO TWEETERS, highs from behind you will only mess up the sound stage and imaging, idealy the "rear fill" speakers would be mids, or mid-bass if no sub is used and the should be in mono. 94

 

A lot of people run infinity speakers off a HU, are most HU amplifiers stable below 4 ohms? Most people say that the infinity speakers can run off 4ohm amp or headunit regardless if it stable below 4 ohms? What kind of front 6.5 speakers do you recommend in the front? I am not planning to run a sub in the rear, what kind of rear mid range/mid bass drivers do you recommend? When you said in mono what does that mean. Oh and I am using a 6 x 8 speaker in the rear because that is the speaker size for my rears.

 

Most HUs internal amps are stable below 4 ohms as long as power and grounds are sufficient, [stock radio harnesses can not supply the current needed for today's "high power" HUs] and definitely not if loaded down to 2 ohms, the other issue is heat dispersion, the lower the load on an amps output, [speaker impedance] the hotter the amp will run and unless the amp is using a regulated power supply the output of the amp, [RMS wattage] is doubled each time the load is halved.

EG; and if your amp is stable below 4 ohms, it will make 4x45W RMS into 4 ohms or 4x90W RMS into 2 ohms.

It is very important to know if the amp is stable below 4 ohms or damage, [due to overheating] will result.
If your owners manual for the amp does not specifically say it is not stable below 4 ohms or use only 4 ohm speakers, then you should have no problem with the Infinity speakers, again... as long as there is current to the amp and cooling airflow is not restricted in any way.

I am not sure about the Alpine KTP-455 because I have not found a spec sheet on them, [not available on the Alpine site]

So question is, what is the MM&Y of car this is going into?

What kind of budget do you have for speakers?

Whatever your budget, spend it on the front speakers, in most cases you can easily get away with stock speakers as rear fill.

Mono is like a sub is driven, either with a one channel amp, [mono block] or a 2ch amp that has been "bridged" into mono, [turned into a 1ch amp] or a 4ch amp that the rear two channels are bridged into one channel.
The two rear speakers are wired in series to increase the impedance and lower the amps output to them, although this can also be done with the amp gain.
I also do not know if that is possible with the Alpine KTP-445.

I am not sure about the Alpine KTP-455, [bridging] because I have not found a spec sheet on them, not available on the Alpine site]

As for what speakers to get, that is kind of up to you, you should go around to your local car audio shops with a CD of your favorite tunes and have a listen to speakers, [with a 45W amp driving them] to get an idea of what diff. speakers sound like, price range is also an issue.

With that said, IMO Infinity makes a pretty good sounding speaker for the price, with a proper install they can sound very good, there are better speakers, even much better speakers, price is a factor, "you get what you pay for". 94

 

When choosing rms speakers it is important that they are suitable to use with your amplifier or head unit. If they are not suitably matched the speakers could draw too much current and damage equipment. And also for sub woofer, It is built a lot stronger and can handle a lot more power. Its aim to get a sub with a high RMS power.